Lift systems for positioning and carrying impact attenuation cushions are well known in the art. A variety of different types of lift systems exist. One such apparatus is shown in FIG. 7 (prior art) which shows a hydraulic lift system coupled to the rear of a mobile vehicle such as a truck. The lift is attached to the truck by a series of welds and bolts and operates to pivot the attenuation cushion 28 between a substantially horizontal position parallel to the road surface, and a vertical position perpendicular to the longitudinal axis of the truck. The lift apparatus operates to place the impact attenuation cushion in the vertical or "non-operational" position to enable transportation of the device. Such a system is described in commonly assigned U.S. Pat. No. 5,697,657 entitled VEHICLE MOUNTED CRASH ATTENUATION SYSTEM, and incorporated herein by reference. In the above-identified patent, the carrying surface 78 operates to engage a bottom surface of the attenuation cushion, and includes a series of through holes for receiving bolts so as to enable the attenuation cushion to be bolted to surface 78 at a plurality of locations. The carrying surface 78 and corresponding cushion 28 operate via hydraulics to pivot about the transverse or z-axis to either the horizontal (deployed) or vertical (non-operational) position. A similar prior art design is illustrated in FIG. 8 and described in U.S. Pat. No. 5,642,792 entitled HIGHWAY CRASH CUSHION issued Jul. 1, 1997 to David L. James and assigned to Energy Absorption Systems, Inc.
As shown in FIG. 8, a truck mounted attenuator cushion 12 includes an attachment frame 78 which is pivotably mounted to a front section 16 to pivot about pivot axis 80. A hydraulic actuator 82 mounted between the front section 16 and attachment frame 78, extends and/or retracts so as to tilt the TMA unit 12 to the vertical/or horizontal stage position.
However, significant problems exist with these designs. First, the hydraulics unit operates not only to pivot the attenuation cushion, but also operates to hold the cushion in place, causing severe stress and wear on the actuator. Moreover, in prior art lift assemblies, the attenuator cushion is suspended from, rather than resting on, or supported by, the lift apparatus. This suspension causes increased tension on the hydraulics as well as on portions of the lift apparatus, resulting in increased wear and early failures for these lifts. Furthermore, the structural characteristics and architecture of the prior art lift assemblies have resulted in rotation of the lift apparatus between a horizontal and vertical crash cushion position such that the distance of the crash cushion from the ground when placed in the vertical position is significantly higher than when in the horizontal position. The combination of the relative height from the ground and "suspension" of the impact cushion leads to undue sway or lateral displacement (i.e. rocking) of the impact cushion during transportation, often resulting in damage to the cushion, even at relatively low speeds (e.g. 10 mph). Thus, when such a cushion is transported over any relatively long distance (e.g. 100 miles) the cushion may break or suffer structural damage as a result of its inherent instability, when suspended on prior art lift devices.
Accordingly, it is highly desirable to obtain a lift apparatus which operates to carry and support rather than suspend the impact attenuation cushion to minimize lateral displacement and to eliminate structural support of the cushion by the hydraulics, thereby preventing undue strain and wear on the cushion, as well as on the hydraulics.